Facilitating nitrogen accessibility to boron-rich covalent organic frameworks via electrochemical excitation for efficient nitrogen fixation

摘要

Covalent organic frameworks with abundant active sites are potential metal-free catalysts for the nitrogen reduction reaction. However, the utilization ratio of active sites is restricted in an actual reaction process due to the limited nitrogen transport. Here, we demonstrate that facilitating the N2 accessibility to boron-rich covalent organic frameworks through electrochemical excitation can achieve highly efficient nitrogen reduction activity. Simulations show that the boron sites are bonded with nitrogenous species under electrochemical condition and the resultant amorphous phase of covalent organic frameworks has much stronger affinity toward N2 to enhance the molecule collision. Combined with experimental results, the excitation process is confirmed to be a virtuous cycle of more excited sites and stronger N2 affinity, which continuously proceed until the whole system reaches the optimum reaction status. As expected, the electrochemically excited catalyst delivers significantly enhanced reaction activity, with a high Faradaic efficiency of 45.43%.